Abstract
Commercial TiO2 (anatase) was successfully modified with Ag nanoparticles at different nominal loadings (1%–4%) using a liquid impregnation method. The prepared materials retained the anatase structure and contained a mixture of Ag0 and AgI species. Samples exhibited extended light absorption to the visible region. The effect of Ag loading on TiO2 is studied for the photocatalytic reduction of CO2 to CH4 in a gas–solid process under high-purity conditions. It is remarkable that the reference TiO2 used in this work is entirely inactive in this reaction, but it allows for studying the effect of Ag on the photocatalytic process in more detail. Only in the case of 2% Ag/TiO2 was the formation of CH4 from CO2 observed. Using different light sources, an influence of the localized surface plasmon resonance (LSPR) effect of Ag is verified. A sample in which all Ag has been reduced to the metallic state was less active than the respective sample containing both Ag0 and Ag+, indicating that a mixed oxidation state is beneficial for photocatalytic performance. These results contribute to a better understanding of the effect of metal modification of TiO2 in photocatalytic CO2 reduction.
Highlights
In recent decades, atmospheric CO2 concentration has been increasing annually mainly due to the extensive use of fossil fuels [1,2]
All investigated Ag/TiO2 materials have been successfully prepared by facile impregnation methods
One explanation for this higher photocatalytic activity may be the presence of a Ag2 O–TiO2 interface that may act as an e- trapping layer compared to the pure Ag0 loaded sample
Summary
Atmospheric CO2 concentration has been increasing annually mainly due to the extensive use of fossil fuels [1,2]. The noble metal deposition has attracted a lot of attention since it can improve e− –h+ separation and enhance the semiconductor’s absorption in the visible light region [26,27] Noble metals such as Au, Pt, Ag, Pd, Rh, and coinage metals such as Ni etc., have lower Fermi levels than TiO2. The localized surface electron plasmon resonance effect (LSPR) induced by noble metals contributes to the activation of TiO2 absorption in the visible region of the light spectrum. The assessment of the photocatalytic CO2 reduction activity of the aforementioned materials, the study of the influence of Ag loading, and the effect of mixed Ag species and the LSPR on the products’ concentration was carried out in a high purity gas-phase photoreactor
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